Heat 1½ tsp. oil in medium skillet over medium-high heat. Add onions, bell pepper and garlic. Cook, stirring occasionally, until onions and pepper soften, about 7 minutes; set aside.
In medium mixing bowl, add black beans, refried black beans, cooked brown rice, corn, pimientos, cilantro, Adobo and reserved onion mixture. Using clean hands, mix thoroughly until combined. Divide bean mixture into 8 portions; using hands, form into 8 patties. Wrap each patty in plastic wrap; transfer to freezer until firm, about 20 minutes. (Note: Black bean patties can be stored, wrapped and frozen, for up to 6 months).
Heat remaining oil in same skillet over medium-high heat. Add black bean patties, making sure not to crowd pan. Cook, flipping once, until dark golden brown on both sides and warm in center, 10-12 minutes.
To assemble burgers, place black bean patty on bottom hamburger bun. Top with avocado and pico de gallo. Serve.